Typically, printing of a web for a horizontal form-fill packaging machine has included a platen press. Printing of the packaging web could be accomplished at a speed of 12-15 imprints per minute. The relatively slow speed involved was required to obtain proper alignment of the press with the moving web and the requirement for an even printing contact of the platen press with the web. Characteristically, the resultant printed web was of a poor quality.
Further, due to the long dwell time of the ink on the printing plate between impressions, a slow-drying ink was required. The slow-drying ink limited the characteristics of the web used, typically limiting the web to an absorbent film, such as a paper web, which could absorb the slow-drying ink. This, however, precluded the use of a platen press on non-absorbent film or foil which required quick-drying ink which would dry by evaporation only.
A proposed solution to overcoming the difficulties encountered by the use of platen presses has been the use of flexographic printers using a liquid ink as compared to a paste ink typically associated with platen presses. Traditional flexographic printers are driven entirely mechanically through a single drive system. A standard fixed speed DC motor is used and elaborate controls required to match the speed of printing with the speed of the web.
All flexographic printers consist of a print cylinder, printing plate, anilox roll, fountain roll, ink fountain, ink and impression roll, and operate in the following manner: The ink fountain is filled with enough ink to wet the bottom of the fountain roll which is positioned in the fountain. As it rotates, ink is picked up on the fountain roll and transferred to the anilox roll which is positioned parallel to it. The combination of the type of engraving on the anilox roll and the amount of squeeze between the anilox roll and the fountain roll determines the volume of ink transferred. As the anilox roll and print cylinder rotate, the ink is transferred to the printing plate which is mounted to the surface of the print cylinder. The web, which is positioned between the print cylinder and the impression roll, is printed when the print cylinder and inked printing plate roll over the web and transfer the message on to the web.